public bool DeleteDocument(Document doc)
        {
            try
            {
                CurLesson.Documents.Remove(doc);
                Helper.Session.DbContext.Delete(doc);

                return true;
            }
            catch
            {
                //An error occured while deleted the document record
                return false;
            }
        }
        /// <summary>
        /// Add a document to the current lesson
        /// </summary>
        /// <param name="filename"></param>
        /// <param name="filepath"></param>
        /// <returns></returns>
        public Document AddDocument(string filename, string filepath)
        {
            try
            {
                Document newDoc = new Document();

                newDoc.ID = Guid.NewGuid();
                newDoc.Filename = filename;
                newDoc.FilePath = filepath;

                newDoc.Lessons.Add(CurLesson);
                CurLesson.Documents.Add(newDoc);

                NotifyPropertyChanged("Documents");

                return newDoc;
            }
            catch
            {
                //An error occured while creating the new document
                return null;
            }
        }